Method of making a brick with wear indicator

ABSTRACT

A method of making a brick with a color indicator is provided. The brick is particularly useful in the lining of a ball mill to indicate when the liner has worn to the point of possibly failing. Preferably, colored inserts are made of the same refractory material as the bricks but have a coloring material added thereto, thereby minimizing contamination of the material being ball milled. The brick and the insert are formed under the same pressures to provide similar shrinkage characteristics and the brick and insert are then fired together at an elevated temperature.

United States Patent lnventor Robert F. Rea

Bloomfield Township, Mich. Appl. No. 797,414 Filed Feb. 7, 1969 Division oi'Ser. No. 533,033, Mar. 9, 1966 Patented Nov. 9, 1971 Assignee Champion Spark Plug Company Toledo, Ohio METHOD OF MAKING A BRICK WITH WEAR INDICATOR 7 Claims, 5 Drawing Figs.

US. Cl 264/56, 264/60, 264/65, 264/148, 264/263, 264/271 Int. Cl ..C04b33/32, C04b 35/64 Field of Search 52/596;

[56] References Cited UNITED STATES PATENTS 1,198,940 9/1916 McGiehan 52/596 1,439,410 12/1922 Gray 52/596 1,775,396 9/1930 .lackman et a1 52/596 2,184,601 12/1939 Konopicky 52/596 2,274,907 3/1942 Madala 52/596 Primary ExaminerDonald J. Arnold Att0rney0wen and Owen ABSTRACT: A method of making a brick with a color indicator is provided. The brick is particularly useful in the lining of a ball mill to indicate when the liner has worn to the point of possibly failing. Preferably, colored inserts are made of the same refractory material as the bricks but have a coloring material added thereto, thereby minimizing contamination of the material being ball milled. The brick and the insert are formed under the same pressures to provide similar shrinkage characteristics and the brick and insert are then fired together at an elevated temperature.

METHOD OF MAKING A BRICK WITI-I WEAR INDICATOR This application is a division of my copending application, Ser. No. 533,033 filed Mar. 9, I966.

This invention relates to a method of making a brick havingmeans to indicate when a predetermined amount-of wear of thebrick-has occurred.

A brick according to the invention'is particularly useful in the liner of a ball mill 'container wherein the liner is subjected to wearwhile the ball mill-is operated. In a ball mill, the rate of wear of the. liner is difficult to determine and can varygreatly according to such factors as the type and amount of the charge and the percent of solids therein, the size, density, hardness,

and quantity of mill balls, and the rate of revolution of the ball.

mill container. It is also difficult to determine the amount of vvear,.as by measuring the interior. of the ball mill container, because:the wear varies considerably for different portions of the container. Such measurements are also difficult to obtain because more than half of the volume of the millcontainer is normally-filled with mill balls. An accurate measurement, consequently, is only possible byremoving many of the millballs. This requires considerable labor and time, particularly in larger mills which may contain severaltons of the-mill balls. Consequently, it is easy for the liner to wear, before being noticed, to the extent that portions break away andcontaminate the charge. The wear also may beenough that the outer wall of the container is exposed and worn'by the mill balls to the point of contaminating the charge or even causing failure of'the wall eventually.

The present invention relates to a method of making marking bricks for a ball mill liner, the bricks having indicators or inserts which, when exposed, indicate to the operator that'the liner has worn a predetermined amount. The marking bricks withthe wear indicators neednot be placed throughout" the liner but only in strategic=locations where wear. is greater, min a predetermined pattern in the-liner to-provide a-representation of the wear. Either arrangement keeps the cost ofthe. liner at a. minimumzbecause. the marking bricks, whichv are. more expensive, are used only to the extent necessary. Also, the marked or colored'insert of each brick is-only a small'percentagev of the overall brick. This is important where high purity of thecharge is required'since the contamination from the colored insert will be a minimum.

In a preferred form, the coloredinsert of the marking brick is of a: colored ceramic material, the ceramic material being the same as that used in the brick, so that a minimum difference in expansion or shrinkage will occur between the brick andthe insert andialso sothat'the colored material will minimize contamination of the charge, being of the same basic material as the brick.

It is, therefore, aprincipal object of the inventiontoprovide a method of making a brick with a wear indicator.

Many other objects-and advantages of the. invention willbe apparent from the followingdetailed description of preferred embodiments thereof, reference being made to the accompanyingdrawing, in which:

FIG. 1 is a view in perspective,,with parts broken away and with partsin section, of a ball mill having a liner-embodyingthe invention;

FIG. 2 is a fragmentary view in perspective of a container of the ball mill of FIG. 1;

FIG. 3 is a view in perspective of a brick for the liner of the ball mill, which brick hasa colored section therein;

FIG. 4 is a view in perspective, with parts brokenaway and withparts in section, of aslightly modified mill liner brick embodying the invention; and

FIG. 5 is a view in perspective of a modified brick for the liner of the ball mill, which brick has another type of colored section therein.

A ball mill of thegeneral type-for which the brick according to the invention is particularly useful is shown in FIG. 1. The ball mill" basically includes a drive unit for rotating a ball mill container 12 which is rotatably mounted on. bearing units I4 and 16. The container 12 has an outer metal-wall18-and'a liner 20 and circular end walls 22 which also can include outer metal walls and an inner ceramic liner similar to the liner 20. A particularly useful applicationfor the ball mill is in the mixing and grinding of ceramic batch material for spark plug insulators. Such insulators require a high degree of purity as well as a high degree of uniformity. Consequently, the materials must be mixed for long periods of time andmust be subjected to minimum contamination fromthe ceramic liner 20. In the event that the liner 20 becomes too thin during use, portions thereof can break away and contaminate the ceramic batch material'so as to impair the quality of the final spark plug or other product made with the ceramic material. The wear also can be excessive to the point that the-outer metal wall 18 is exposedwith small pieces of metal being worn away and contaminating the batch. Over a period of time this wear even can cause failure of the outer wall- 18 and result in expensive repairs for the ball mill. The extent of the wear of the liner 20 cannot-be accurately determined by the length of-time the ball mill is in use because the wear varies greatly. As pointed out previously, thedegree of wear will depend'on the type and amountof the charge, and percent of solids, as well as the size,

density,.hardness, and quantity of the mill-balls employed. The rate of. revolution-of the ball mill container l2also is a factor in the, rateof wear. Attemptshave been made heretofore to determine theamount of wear'of theliner by taking diametrical measurements in the container 12. This has not been reliable or practicaLhowever, because the wearin the container is not at all'uniform and because the measurements are difficult and time consuming to obtain, due to the presence of the mill balls.

To overcome the above problems,-marking bricks 24 are used as part of the liner 20. [none form ofthe invention, the brick 24, as shown in FIG. 3, is of generally rectangular configuration with slightly tapered sides to fit properly in the cylindricalinterior of the wall 18. In.a,rear surface of the brick 24 is a transverse groove 26 extending completely acrossthe brick and containinga colored'marking section or insert 28.

The height of the section 28 should be such that whenthe section is exposed after the brick wears sufficiently, the thickness of thetoveralljbrick will still be, sufficient that the liner will not. break away. and contaminate the batch material'being ground and mixed The-height of the section willbefrom one-eighth. to one-third the height of the brick 24 and usually will be from about one inch to about three inches thick. The width and length: of the colored' section 28.arenot critical but these dimensions should be small to.minimize contamination, and

yet. be clearly visible when exposed. If desired, however, the colored section. can constitute a layer extending over. the entireback of the'brick.

The colored section 28 is preferably made of the same I material as the brick. but with a colorant, preferably a strong one, added. By way of example, cobalt oxide or chromium oxide are desirable for alumina brick. However, small amountsof oxides of manganese, iron, or nickel, or any combination, can, also be used. Other colorants also can be used but are usually more costly than. thosejust set forth. Examples aretitanium, vanadium, and copper compounds. The colored sections=canalso be made by adding carbon or metals to the ceramic andfiring in an inert atmosphere. Amounts of about one-half percent to about two percent, by weight, of the colorants added=to the ceramic material are, usually sufficient. By making-the section 28 of the same material as the brick, the effect of contamination is minimized. since the contaminating colored material is the same as that of the brick except for the additional-colorant.

By way. of example, the brick and the insert can have the following compositions:

Bentonite Cobalt Oxide Moisture in the amount of l2 percent by weight can be added to the batches and the final shaped brick and insert then fired to cone 16, for example, for vitrification.

The brick 24 of FIG. 3 can be extruded in a continuous body and then cut transversely to the predetermined brick length. The colored section 28 also can be extruded separately and then cut transversely into sections equal substantially to the width of the slot 26. The slots 26 are then cut in the larger surface of the brick 24 and the colored sections cemented in by means of a thick slip made from crushed, raw brick. The extrusion pressures and other conditions for the brick 24 and the colored section 28 should be alike and the orientation of the brick 24 and the section 28 should be the same to prevent shrinkage cracks which otherwise can occur, particularly since extruded pieces tend to have a high degree of shrinkage. Consequently, if the brick 24 is extruded lengthwise, then the colored sections 28 should be extruded in widths equal to the widths of the brick 24 or the length of the slot 26. The extruded colored section is then cut transversely intosections equal to the widths of the slots 26.

The bricks 24 need not be used throughout the liner but can be employed only at strategic positions or in a predetermined pattern as shown in FIG. 2. In this manner, a minimum number of the more expensive marking brick 24 need be employed and contamination by the exposed coloring section is a minimum. By way of example, it is sufficient to have less than one out of ten of the bricks in the liner 20 be a marking brick. The mill lining wear is usually considered to be about one percent of the charge being milled. Further, if the marking section 28 includes two percent of the colorant and occupies ten percent of the area of the brick, the resulting contamination, even if all of the colored section 28 were exposed, would only be 0.0002 percent. As a practical matter, the liner would be replaced when only a relatively few of all of the colored marking sections 28 were exposed.

Another suitable marking brick 30 is shown in FIG. 4. This brick has a cylindrical recess 32 in which a cylindrical marking section or insert 34 is located. The section 34 can be pressed to shape under a predetermined pressure and then placed centrally in a larger mold cavity with the uncolored ceramic material pressed around it. By shaping both pieces at the same pressure, the problem of shrinkage cracks again can be minimized.

A marking brick 36 of FIG. has a recess 38 in which a marking section or insert 40 is located. The brick 36 can be either extruded in accordance with the method discussed for the brick 24 or can be molded in accordance with the method discussed for the brick 30. The important feature of the brick 36 is that the sides of the insert 40 extending toward the face of the brick taper so that more of the colored section is exposed as more of the brick wears. In this manner, the amount of wear can be determined by the width of the exposed colored section. The thickness of the section 40 may exceed that of the sections 28 and 34 but again will not normally exceed approximately one-third the thickness of the overall brick.

While the section 40 is shown in an elongated shape, it also can be made in the form of a cone or pyramid, if the brick is molded similarly to the brick 30. The sides of the section 40, rather than tapering toward one another, in a direction toward the face of the brick, can taper in the opposite direction so LII that the exposed portion narrows as wear increases.

Various modifications of the above described embodiments of the invention will be apparent to those skilled in the art, and it is to be understood that such modifications can be made without departing from the scope of the invention, if they are within the spirit and the tenor of the accompanying claims.

I claim:

1. A method of making a ceramic marking brick for use in the liner of a ball mill to indicate the extent of wear of the liner, wherein the bl'lCk has a front surface for exposure to the interior of the ball mill and a back surface spaced from the front surface, said method comprising preparing a batch of ceramic material, forming the batch material into a brick under pressure, forming a recess centrally in the back surface of the brick to a predetermined depth, preparing a batch of colored ceramic material the same as the batch material of the brick with the addition of a colorant, forming the colored batch material into an insert of the same size and shape as the recess under substantially the same pressure used to form said brick, affixing said insert in said recess by preparing a slip of the batch material ,of the brick and locating the slip between the insert and the recess to affix the insert in the recess, and firing the combination brick and insertto a predetermined temperature.

2. A method of making a marking brick for use in a liner of a ball mill to indicate the extent of wear of the liner, wherein the brick has a front surface for exposure to the interior of the ball mill and a back surface spaced from the front surface, said method comprising preparing a batch of a ceramic material, forming said batch material into a brick under a predetermined pressure, forming a groove in a rear surface of said brick, preparing a batch of colored ceramic material the same as the batch material of the brick with the addition of a colorant, extruding a bar of said colored batch material having a predetermined cross-sectional size and shape, cutting said bar. to fit the groove of said brick, affixing said bar in said groove by preparing a slip of the batch material of the brick and locating the slip between said bar and said groove to affix said bar in said groove, and firing the combination to a predetermined temperature.

3. A method according to claim 2 characterized by forming said brick by an extruding step and cutting the extruded material to a predetermined length.

4. A method according to claim 2 characterized by forming the groove in the rear surface of the brick to a depth from oneeighth to one-third the thickness of the brick.

5. A method of making a ceramic marking brick for use in a liner of a ball mill to indicate the the extent of wear of the liner, wherein the brick has a front surface for exposure to the interior of the ball mill and a back surface spaced from the front surface, said method comprising preparing a batch of ceramic material and a colorant, pressing the material into an insert of a predetermined shape, placing said insert in a mold cavity, preparing a batch of ceramic material the same as that of said insert except for said colorant, pressing the latter batch into a brick on said insert under the same amount of pressure used to form said insert, and tiring the combination brick and insert.

6. A method according to claim 5 characterized further by placing the insert centrally in the mold cavity and pressing the latter batch over and around said insert.

7. A method according to claim 1 characterized by preparing the batch of ceramic material and the batch of colored ceramic material with a high alumina content. 

2. A method of making a marking brick for use in a liner of a ball mill to indicate the extent of wear of the liner, wherein the brick has a front surface for exposure to the interior of the ball mill and a back surface spaced from the front surface, said method comprising preparing a batch of a ceramic material, forming said batch material into a brick under a predetermined pressure, forming a groove in a rear surface of said brick, preparing a batch of colored ceramic material the same as the batch material of the brick with the addition of a colorant, extruding a bar of said colored batch material having a predetermined cross-sectional size and shape, cutting said bar to fit the groove of said brick, affixing said bar in said groove by preparing a slip of the batch material of the brick and locating the slip between said bar and said groove to affix said bar in said groove, and firing the combination to a predetermined temPerature.
 3. A method according to claim 2 characterized by forming said brick by an extruding step and cutting the extruded material to a predetermined length.
 4. A method according to claim 2 characterized by forming the groove in the rear surface of the brick to a depth from one-eighth to one-third the thickness of the brick.
 5. A method of making a ceramic marking brick for use in a liner of a ball mill to indicate the the extent of wear of the liner, wherein the brick has a front surface for exposure to the interior of the ball mill and a back surface spaced from the front surface, said method comprising preparing a batch of ceramic material and a colorant, pressing the material into an insert of a predetermined shape, placing said insert in a mold cavity, preparing a batch of ceramic material the same as that of said insert except for said colorant, pressing the latter batch into a brick on said insert under the same amount of pressure used to form said insert, and firing the combination brick and insert.
 6. A method according to claim 5 characterized further by placing the insert centrally in the mold cavity and pressing the latter batch over and around said insert.
 7. A method according to claim 1 characterized by preparing the batch of ceramic material and the batch of colored ceramic material with a high alumina content. 